Hundreds of detection devices that make use of radio frequency, have been developed for use in various detection applications, such as tracking animals, for identification of humans within secure areas, and for remote data logging and data collection, tracking of freight, payment of tolls on toll roads. Some of these devices are called RFID Tags, or RF Tags and are often designed to replace fixed barcodes or ID's in many processes. RFID and RF Tags can be categorized into two separate types:
RFID Tags are passive, and can be typified as low cost (as low as 10 cents), fixed ID, disposable and usually short range. Some are long range but can have only a single tag in the reading field. However, anti-collision methods can be used to read with groups of up to 500 tags within a reading field and it is possible to extend the detection range to miles. RFID detection tags work in frequency ranges of 100 Khz to 3 Ghz. (see U.S. Pat. No. 5,517,188, incorporated herein by reference).
RF Tags are active. They typically add a battery to the typical RFID design discussed hereinabove to enable longer reading ranges without powerful readers, and to enable digital clocks, memory, optional programmable ID. Cost can be as high as $1,000 and as low as $5, typically priced in range of $40. They typically work in a frequency range of 15 Mhz to 3 Ghz.
RFID tags and RF tags both operate as transponders—like an electronic mirror. The basic operating principle is that energy from the antenna of the reader generates an electro-magnetic field, which induces a voltage in the coil of the tag and supplies the tag with energy. Data transmission from the reader to the tag is done by changing one parameter of the transmitting field (amplitude, frequency or phase) and reflected back. The tag digitally communicates back to the reader by reflecting the electro-magnetic filed back to the transmitter.
In most cases RFID and RF tags have a fixed ID which cannot be altered. The electronic reader is placed in critical area where it can read this ID when the tag is activated by the reader, in much the same way as a barcode is scanned by a barcode scanner at a supermarket. In some cases the RF tag can be programmed providing it is removed to an isolated area so that the programmer sees only a single tag, or the providing programmer has prior knowledge of the fixed ID contained in the tag, or a special encoded signal is used for programming (see U.S. Pat. No. 5,517,188, incorporated herein by reference).
These “transponder tags” all have many advantages. The RFID passive versions can cost as low as 10 cents and can, in effect, replace paper barcodes (see U.S. Pat. No. 6,280,544, incorporated herein by reference). The range and distance to read a tag is determined by the tag size and the power and frequency of the signal from the reader. It is possible to develop specialized high frequency transponder tags that can be read from miles away with a powerful high frequency signal or even from a radar scan. A stand-alone transmitting tag with its own transmitter, instead of modulation of a reflective high frequency signal would consume far too much power, for these long range applications. Low frequency (50 Khz to 500 Khz) transponder tags have short ranges, but may have cost advantages and may be readable even when attached to metal shipping containers or steel railroad cars. In most tracking applications a standalone two way transmitter and receiver as opposed to a transponder based system used in RF Tags and RFID tags would have too many disadvantages: too expensive, limited range, and require complex transmission RF circuitry, including crystals, and have high power consumption since all transmission power must come from the tag as opposed to the reader's interrogation signal.
A major disadvantage of all transponder based tag designs is that special anti-collision methods (see U.S. Pat. Nos. 6,377,203; 6,512,478; 6,354,493; 5,519,381, all incorporated herein by reference) must be used to read more than one tag within a reader's transmitted field, or alternatively a short range reader must be used to individually address each tag within the larger field (see U.S. Pat. No. 6,195,006, incorporated herein by reference). Also, to program a RF tag requires either a special signal and the tag must be isolated from other tags (only one in the field) or special hardware must be used. This makes difficult any “networks” of tags and real time inventory or automated real-time detection and tracking of many items all contained within a truck or warehouse for example difficult. It also makes impossible a network of interactive tags able to freely transmit, be programmed and receive as is the case in any conventional network, and the possibility of real-time freight tracking using the internet is difficult. A second major disadvantage is that to obtain long ranges (100–1,000 feet), higher frequencies are required, and these lead to high power consumption. This power may come from higher activation power of the transmitter signal to the RFID transponder, or from a battery contained within the RF transponder. The batteries are high capacity large (e.g. AA or C alkaline) and life is limited in these applications. Either special measures must be used to either conserve battery life (see U.S. Pat. No. 6,329,944, incorporated herein by reference) or special methods must be used that minimize power for even simple things like clocks or timers (see U.S. Pat. No. 6,294,997, incorporated herein by reference) in RFID or RF Tags.
Finally, active RF tags are typically larger (½ inch thick 4″×5″) and expensive (over $50/unit) because of the battery size. Thin versions typically have limited battery life (two years). Active tags may be use to locate the palett or shipment within a warehouse, as well as for tracking its progress through a supply chain. Several tags have been developed to include limited data tracking as well as the ability to remotely transmit the data. These tags however do not contain LED's or Displays buttons of any kind, and again represent, in effect, electronic smart barcodes.